Flexography is a rotary contact relief printing method that utilizes a relief master plate made of a flexible rubber like material as an imaging source. Flexographic printing offers several advantages over other printing techniques including good substrate latitude due to the soft master plate, very high speed, (often 100's of feet of printed matter per minute) and good quality when used with viscous pigment based inks. Flexography is widely used for printing packaging materials and continues to gain market share in the printing market.
Gravure (intaglio) printing is a recess printing method where the printing surface such as a printing plate has recessed regions such as wells. The surface receives ink and a blade removes any excess ink, so that only the wells retain ink. A high applied contact pressure presses the printing surface against a substrate to be printed transferring the ink in the wells to the printing substrate. Typical printing substrates include paper, transparency, foils, plastics, etc. However, due to the high contact pressure, generally, gravure printing processes print to paper or relatively sturdy substrates.
Despite their speed and high quality, flexography and gravure have not been used for low volume printing because patterning the traditional master plate is a slow and expensive process that can take hours for a single plate. As a result, master plates are expensive. Once imaged, the master plate cannot be easily re-imaged or re-used. Thus, unless a long run of identical copies is needed, the cost of manufacturing a master plate cannot be justified.
Various techniques have been attempted to circumvent this problem. In U.S. Pat. No. 6,234,079 by R. Chertkow, a re-usable print plate is proposed using various techniques including electrostatic, shape memory alloys, electromagnetic and other contact means to adjust the print surface. However, most of the techniques are difficult to implement. For example, generating magnetic fields sufficient for actuation using coils involves high currents. Furthermore, the coils are difficult to fabricate. Patent application WO 2002051639 entitled Digital Printing Device and Method by S. Kaplan proposes a re-usable print plate using local heating of liquids that expand or vaporize under a membrane to create a relief printing surface. However, fabricating a printing plate with an array of heater elements corresponding to print pixel locations, each heater element to expand or vaporize liquids as proposed by Kaplan is expensive. Alternative approaches for localized heating of liquid near each pixel such as using high power laser sources are also expensive and this limits the market size for such a device.
Thus, an improved method of forming and actuating a printing plate for use in digital recess or relief printing is needed.